linux-kernel - Re: [PATCH 0/3] condition EAS enablement on FI support

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Message-ID: <20200924160846.GB17927@arm.com>
Date:   Thu, 24 Sep 2020 17:08:46 +0100
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     Quentin Perret <qperret@...gle.com>
Cc:     mingo@...hat.com, peterz@...radead.org, vincent.guittot@...aro.org,
        catalin.marinas@....com, will@...nel.org, rjw@...ysocki.net,
        viresh.kumar@...aro.org, dietmar.eggemann@....com,
        valentin.schneider@....com, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] condition EAS enablement on FI support

On Thursday 24 Sep 2020 at 14:37:27 (+0100), Quentin Perret wrote:
> On Thursday 24 Sep 2020 at 13:39:34 (+0100), Ionela Voinescu wrote:
> > Given the maturity gained by cpufreq-based Frequency Invariance (FI)
> > support following the patches at [1], this series conditions Energy
> > Aware Scheduling (EAS) enablement on a frequency invariant system.
> > 
> > Currently, EAS can be enabled on a system without FI support, leading
> > to incorrect (energy-wise) task placements. As no warning is emitted,
> > it could take some debugging effort to track the behavior back to the
> > lack of FI support; this series changes that by disabling EAS
> > (and advertising it) when FI support is missing.
> > 
> > The series is structured as follows:
> >  - 1/3 - create function that can rebuild the scheduling and EAS'
> >    performance domains if EAS' initial conditions change
> >  - 2/3 - condition EAS enablement on FI support
> >  - 3/3 - arm64: rebuild scheduling and performance domains in the
> >          case of late, counter-driven FI initialisation.
> 
> I'm still reading through this, but shouldn't patch 2 and 3 be swapped?
> Otherwise we have a weird state at patch 2 where EAS will fail to start
> (IIUC), which might not be ideal for bisection.
> 
> Thoughts?

I probably invented myself reasons for not doing it, like: without 2/3,
3/3 does not make any sense having and the scenario at 3/3 is currently
unlikely.

But it would definitely make it safer, so I'll change the order.

Thanks,
Ionela.

> 
> Cheers,
> Quentin